Research on Sediment Transport Rate in Surf Zone by Taking Account of Liquefaction and Fluidization of Sand Layr

本研究针对碎波带泥沙运动的一种典型型态-层状运动（片流）进行探讨。研究目的是为了弄清孔隙水压力和垂向有效应力变化对成层运动的影响，建立本构方程，得到碎波带输沙率的变化规律，以便在实验室内再现正常沙床中孔隙水压力的变化。需要同时产生与实际海岸中的海床上的波浪压力和振荡流一样大的水压力变化和振荡流。为此，研制了一种两端封闭的U形振荡管。遗憾的是，由于有限的预算，所需的大的压力变化和振荡流和压力和流量之间的相位的自由控制不能得到。孔隙水压力的变化，在一个薄层的砂床表面以下10 cm，这是重要的分层运动，测量在这个管中只有一个水压变化。将测量结果与近似解进行了比较，并对近似解中的常数进行了讨论。同时，还测量了砂床上的块体在水压变化和管内振荡流作用下的沉降。本文还讨论了波浪压力和振荡流对沉降的影响。其中，一种新的更有效的振荡管开发。目前，利用这种新型管对碎波带泥沙输移规律的研究仍在继续。一种新的数值模拟技术也正在通过应用所谓的离散单元法而得到发展。

In this research, the layred motion ( sheet flow ), which is a typical type of sediment motion in surf zone, is treated. The purpose of the research is to make clear the effects of the porewater pressure and the vertical effective stress variation on the layred motion, find the constitutional equations and obtain a law of sediment transport rate in surf zone.In order to reproduce the porewater pressure variation in a normal sand bed in laboratory, it is necessary to generate simultaneously a water pressure variation and a oscillatory flow as large as the wave pressure and the oscillatory flow on seabed in actual coast. For this purpose, an oscillatory tube of U shape with both ends closed was developed. Unfortunately, with the limited budget, the desired large pressure variation and oscillatory flow and a free control of the phase between the pressure and flow could not be obtained.The porewater pressure variation in a thin layr of 10cm below the sand bed surface, which is important for the layred motion, was measured under only a water pressure variation in this tube. The measured results were compared with an approximate solution, and the values of constants in the solution were discussed. Also the subsidence of a block on a sand bed was measured under a water pressure variation and an oscillatory flow in the tube. The effects of the wave pressure and the oscillatory flow on the subsidence were discussed.Several other works were done. Among them, a new more effective oscillatory tube was developed. At present, the research is continued using this new tube to obtain the law of sedimenet transport rate in surf zone. A new numerical simulation technique is also being developed by applying the so-called distinct element method.